To understand the mechanisms of gene expression in higher organisms we have chosen to study two sets of coordinated gene responses in Drosophila: 1) the production of muscle-specific proteins in myogenesis and 2) the "heat shock" response induced in both eukaryotic and prokaryotic cells by a variety of environmental stresses. Both of these phenomena are useful experimental systems for study of the kinds of genetic activity that occur during differentiation in eukaryotes. In addition, myogenic differentiation is an important developmental process in its own right and the heat shock response appears to be an important homeostatic mechanism in all cells. We will extend our studies on the molecular mechanism of the translational control of gene expression in heat shocked cells. To determine the features by which heat shock mRNAs are recognized by the translation machinery we will construct, by recombinant DNA technology, hybrid genes with features of control and heat shock genes. Translational control of the resulting hybrid mRNAs will be tested by transient infection of cultured cells. Identification of the relevant mRNA features will allow us to design experiments to study the elements of the translational machinery involved in mRNA discrimination. One of the largest heat shock puffs, 93D, appears to encode an important, but unidentified, nuclear RNA. We have a cloned DNA segment from 93D. Overlaping clones will be obtained to cover the region. The DNA sequences will be used to study RNA products of this locus in heat shock and in normal development to gain insight into the roles of nuclear RNA. Muscle studies will focus on the gene families encoding the 3 subunits of troponin, tropomyosin and myosin light chains. All of these are involved in regulation of muscle contraction in insects. We have isolated genomic clones for several of these genes. The genes and their protein products will be analyzed and compared with the analogous vertebrate proteins. We will use genetic studies of mutants, deletions and transformation with specifically engineered genes to study the coordinated expression of these genes,, the significance of multigene families, and the production of tissue-specific isoforms of these proteins. Drosophila sequences with homology to human histocompatibility genes are being studied. If expression of these sequences can be detected the genes will be studied by molecular and genetic techniques. One question will be whether the genes provide immunological defense or have evolved some other function such as mediating tissue organization.